Halogenated aromatic polyesters such as the condensation products of 4,4'-isopropylidene-2,2'6,6-tetrachlorodiphenol or 4,4'-isopropylidene-2,2',6,6'-tetrabromodiphenol with isophthalic acid and/or terephthalic acid or the ester-forming derivatives thereof have been used to produce a number of inherently non-burning fibrous materials which are particularly advantageous when fibrous articles are required for use in fire-control environments, such as children's sleepwear, suits for fire fighters, hospital furnishings, and uniforms for military and civilian personnel. However, these halogenated aromatic polyesters are sensitive to organic solvents such as perchloroethylene, which is a commercial dry cleaning solvent.
Copending patent application U.S. Ser. No. 208,364, entitled "Improved Processes for Drawing Halogenated Aromatic Polyester Fibers", filed concurrently herewith by Albert G. Williams, discloses a process for drawing halogenated aromatic polyester fibers at a temperature of from about 315.degree. to about 355.degree. C. at a draw ratio of from about 3:1 to about 10:1 to produce halogenated aromatic polyester fibers having improved tensile properties. To some extent, this drawing process also improves the solvent resistance of the fibers. However, some solvent sensitivity is present even after the halogenated aromatic polyester is drawn at these high draw ratios and elevated temperatures.
U.S. Pat. No. 3,684,766 and U.S. Pat. No. 3,780,148 describe a process for crystallizing a low molecular weight polyester with non-halogenated crystallizing agents prior to a second stage reaction.
The search has continued for methods of improving the solvent resistance of halogenated aromatic polyester fibers. This invention was made as a result of that search.